Deadbolts are engaged by turning a key or knob on the inside of a door and are usually used in conjunction with a lock that engages by the action of a spring. The deadbolt is intended to give an additional measure of protection to occupants of a house or apartment or to their belongings. However, the locks of both a deadbolt and a spring activated lock are subject to being picked. A deadbolt lock, in particular, is usually located in an enclosure on the outside wall of a door or insert into the door and are accessible to be picked by a potential intruder outside the door.
It is known to provide a locking device which prevents the key or knob of a deadbolt from being turned. The devices are positioned on the inside wall of a door and are accessible only to persons inside the door. U.S. Pat. No. 6,301,941 to Nicholsfigueiredo for example describes a bar which slides in a track attached to an inside wall of a door. The bar is in the shape of a yoke which engages the knob of a deadbolt and immobilizes it. The bar only does so however if the track is horizontal. If the bar extends downwardly from the knob, the yoke may slide downward and out of engagement with the knob. If the track extends upwardly from the knob, the yoke may accidently slide downward into engagement with the knob thereby making it impossible to open the door except from inside. If there is no one inside, the door may have to be broken to open it since the door cannot be opened from outside. Even if the track is horizontal the knob must fit into the yoke for the locking device to function properly and if the track shifts over time, the knob may not continue to fit into the yoke.
I have invented a lock for a deadbolt which overcomes many of the shortcomings of the lock described above. The track in which the bar travels may be oriented at any angle on a door so long as the bar when slid forward, contacts the knob. The track can accordingly be positioned so that it avoids decorative moulding or other projections on a door. Furthermore the bar can be immobilized in the track when it is not contacting the knob to prevent the bar from accidently sliding into contact with the knob.
The only way that my lock can be engaged or disengaged is by a person within the premises of a house or apartment. When properly used, the subject lock cannot engage accidently without human intervention and it cannot be engaged or disengaged by someone from outside the premises. As a result, a person cannot accidently lock himself out of a house or apartment since the subject lock can only be engaged and disengaged by him when he is inside the premises.